Hybrid electric vehicles offer reduced fuel consumption and emissions by utilizing both an electric motor/generator and an internal combustion engine and an onboard controller programmed to vary use of each of the engine and motor/generator during different driving conditions to achieve peak efficiency.
One type of hybrid electric vehicle is referred to as a belt-alternator-starter hybrid vehicle. This type of vehicle has a motor/generator operatively connected to an engine crankshaft by a belt and pulley system. The motor/generator is used to start the engine from a key start and may be recharged by the engine during regenerative braking “Key start” or “first start” refers to the engine being started for the first time after the engine has been completely shut off for an extended time. A key start is typically initiated by a vehicle operator inserting a key into the ignition and turning the key to a key-up or further to a key-crank position. This is in contrast to the “quick start” or “restart” which occurs after the engine has been temporarily shutdown by the electronic controller as driving conditions allow, such as when the vehicle is stopped at a stop light. This helps to reduce emissions and increase fuel economy. A high voltage battery (e.g., a 120 volt battery) is typically used to provide sufficient power to accomplish a restart and is also used during regenerative braking.
Most hybrid vehicles also employ a low voltage battery (e.g., a 12 volt battery) to run typical motor vehicle accessories, such as headlights, an audio system, the ECU and other electronic components. The low voltage battery may also be recharged by the high voltage battery (via an auxiliary power module (“APM”), also referred to as a DCDC converter, that converts power from the high to the low voltage) assuming the APM has been activated (which is only after the engine is running). As used herein, “activating” the APM means causing the APM to begin converting voltage from the high voltage level to a lower voltage level, or vice versa.
Different hybrid motor vehicles may utilize the high and low voltage battery systems differently in performing a key start of the hybrid motor vehicle. In one configuration of a hybrid motor vehicle, the high voltage battery is used to perform the key start and the low voltage battery is retained for powering vehicle accessories but is not utilized in the key start process. In another configuration, the low voltage battery is utilized in a key start by supplying power to a starter motor to start the engine, with the high voltage battery utilized for restarts but not for key starts. The low voltage battery also powers the motor vehicle accessories after the key start. In yet another hybrid vehicle configuration, the starter motor initially turns the engine to a first speed during the key start and the motor/generator is powered by the high voltage battery and is then employed in tandem with the starter motor to assist in turning the engine to a final start speed. In some configurations, the APM converts energy stored in the high voltage battery to the voltage level of the low voltage battery when the low voltage battery is used in a key start.